1. Technical Field
The present invention relates to a method for manufacturing a perpendicular magnetic recording medium to be mounted on a magnetic disk device of a perpendicular magnetic recording system, such as a hard disk drive (HDD).
2. Background Art
With increasing capacity for information processing, various types of information recording techniques have been recently developed. In particular, the HDD using a magnetic recording technique has been continuing to increase a surface recording density at a rate of about 100% per year. In recent years, magnetic disks of 2.5 inches in diameter for use in the HDD or the like have been required to have an information recording capacity exceeding 250 Gbyte per piece. An information recording density exceeding 400 Gbit per square inch is required so as to achieve such a requirement. In order to achieve the high recording density in the magnetic disk to be used in the HDD or the like, it is necessary to miniaturize magnetic crystal particles included in a magnetic recording layer for recording information signals, and to decrease the thickness of the magnetic recording layer. However, in a magnetic disk for an in-plane magnetic recording system (which is also referred to as a longitudinal magnetic recording system, or a horizontal magnetic recording system) commercialized in the related art, progress in reducing the size of the magnetic crystal particles would result in degradation of the thermal stability of the recording signals due to a superparamagnetic phenomenon. This generates a thermal fluctuation phenomenon causing the recording signal to disappear, which interrupts an increase in recording density of the magnetic disk.
In order to solve such a cause for interruption, magnetic disks for the perpendicular magnetic recording system have been recently proposed. Unlike the in-plane magnetic recording system, in the case of the perpendicular magnetic recording system, the magnetization easy axis of the magnetic recording layer is adjusted to be directed perpendicularly with respect to the surface of the substrate. The perpendicular magnetic recording system can suppress the thermal fluctuation phenomenon as compared to the in-plane magnetic recording system, and hence is suitable for achieving the higher recording density. For example, Japanese Unexamined Patent Publication No. 2002-92865 discloses a technique regarding a perpendicular magnetic recording medium including a soft magnetic layer, an under layer, a Co-based perpendicular magnetic recording layer, a protective layer, and the like which are formed on a substrate in that order. Further, U.S. Pat. No. 6,468,670 specification discloses a perpendicular magnetic recording medium which has a structure with a continuous layer of an artificial lattice film (exchange coupled layer) exchange-coupled to a particulate recording layer.
Currently, the perpendicular magnetic recording media have been required to have a higher recording density.
The perpendicular magnetic recording medium includes, as main components, a magnetic recording layer formed of hard magnetic material, a soft magnetic (backing) layer formed of soft magnetic material, and an intermediate layer formed of non-magnetic material positioned between the magnetic recording layer and the soft magnetic layer.
Among these layers, the intermediate layer is located under the magnetic recording layer and is a portion serving to control a crystal orientation of the magnetic recording layer and the isolation of a granular structure. In short, the intermediate layer is a very important part as it serves as a base for the magnetic recording layer. Thus, the structure, material, and deposition process of the perpendicular magnetic recording media, and the like have been strenuously studied and developed. As a result, the intermediate layer is divided into a seed layer positioned on the lower side and an intermediate layer (generally also referred to as an underlayer) positioned on the upper side. The intermediate layer (underlayer) includes a lamination of a lower intermediate layer deposited at a low gas pressure, and an upper intermediate layer deposited at a high gas pressure, using the same material. In particular, the upper intermediate layer deposited at the high gas pressure is positioned directly under the granular magnetic recording layer, and thus is a very important part from the viewpoint of controlling magnetic characteristics.